Electrical contact brush



u y 9, 1945- c. G. VAN BRUNT C 2,403,471

ELECTRICAL CONTACT BRUSH Filed June 21', 1941 Inventor Charles G. /ah Brunt;

, by W QJMAH His Att orne gw Patented July 9, 1946 Charles G. Van Brun t, Schenectady,

slg-nor to General] Electric Company, a corporation of New Yor Application June 21, 1941, Serial No. 399,125

14 Claims. (o1..'171 325) My invention relates to electrical contact elements and particularly to improved contact brushes and methods of makinglthe same.

An object of my invention is to provide an improved electrical contact element.

Another object of my invention is to provide an improved electrical contact element formed of a porous block of electrically conductive material provided with a lubricant for the contact surface thereof.

A further object of my invention is to provide an improved method of making an electricalcontact element.

the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming part of this specification.

The single figure in the contact brush for a dynamo-electric machine embodying my invention and made in accordance with my improved method of, manufacture.

It has been found that under normal atmospheric conditions with average humidity, atmos- It has also been found that electrical contact elements made of porous blocks of finely divided electrically conductive material, such as carbon or metal and graphite brushes, tend to wear away very rapidly in dry atmospheres. In the past, different lubricants element, through vibration or otherwise, to form I substances which impede the free movement of the contact element on its guide member or brush holder, thereby decreasing the emciency of operation of the combination. It has been found, however, that by impregnating a, porous block of electrically conductive material with a humectant, such asa polyhydiic alcohol or an alcoholether, or mixtures of these, in at least a portion of the block, lubrication is provided for the contact surface thereof which greatly increases the life of the porous block. Furthermore; I have found that under certain conditions and for certain types of materials, the contact element is drawing illustrates a moves on its described. g

In the drawing, I have shown an electrical contact element includinga porous block III of bonded finely divided electrically conductive macommutator and slip-ring brushes. A terminal clip ii is secured to the porous block In by a rivet l2 and an electrically conductive pigtail member i3 is secured to theterminal clip H and to a connecting terminal element In order to provide a lubricant to the contact surface 15 of the porous block I0, a'portion of the block below the terminal clip ll or the entire a polyhydric alcohol solution. Among the polyhydric alcoholswhich have been found to provide an eilicient lubricant for the contactsurface of the brush Hi, the ethyleneglycols have been found to be particularly eillcient. Mix- I tures of difierent polyhydric alcohols also have have a good lubricating properties. These impregnants are'highlyhygroscopic' and water soluble and relatively wide liquid state temperature Generally, they 'also have the desirable range.

' properties of a relatively high flash polntand 'nant comprising 40% a relatively low vaporpressure at normal contact element operating temperatures. For certain types of electrically conductive materials, such as carbon, electrographitic, or natural graphite brushes, a-solution of from 10% to 30% of nonaethyleneglycol, 1

Hoe-In (enter ng) ajCI-IaOH in water has been found to be a very efllcient impregnant, especially if the metalcontent of the brush is 50% or less. For contact elements wherein the porous material comprises a very large amount of metal, or more, an. impregto 60% nonaethyleneglycol and 20% to 30% polvolefin lycol inwater is a very efilcient lubricant.

In forming my improved contact elements, it has been found desirable to desas the porous 7 It for conducting current between a brush holder connector and the contact element block l9.

porous block ill is im- 7 pregnated with a hygroscopic material, such as removed from the block,

relatively thin coating of material, which does impregnant and is otherwise a solution of 'ment, a part or soluble cellulose acetate dissolved in the block by subjecting it and then impregnating the degassed block with the lubricant, after which excess impregnant is and, in certain cases, a

not react with the stable under operating conditions, is applied to the sides of the dried block. In degassingv the porous block, the contact element is immersed in the impregnant, such as a 20% to 40% solution of nonaethylene glycol in water or benzene, and the block is subjected to a relatively low pressure in this solution for one to two hours,

such that the water or benzene boils, removing the gas from the porous block. After thistreatthe whole of the porous block is impregnated at substantially atmospheric pressure with a solution ofpolyhydric alcohol in water or benzene for from one to two hours. Excess impregnant then is removed from the outside of the block in any suitable manner, as by wiping or draining. The block dried at a temperature between 70 to remove excess water from the brush. As

' stated above, with certain porous materials, it

is desirable to provide a very thin coating of nonpaste forming material .over block. I have found that a thin coating of certain lacquers applied to the sides of the block provides an efllcient surface which will not react.

with the impregnant or other adjacent materials,

even after long periods of use and vibration over will effeca-supporting or guiding surface and tively prevent the penetration or exudation of impregnant through the coating. This lacquer preferably is of an air-drying type, such as acetonesoluble cellulose nitrate or cellulose acetate, which provides a relatively low-friction guiding I surface for the brush on' its brush holder and effectively prevents sticking of the brush in'the holder. I have found that a lacquer having a viscosity of three r four times that of water provides a very satisfactory coating. Acetonein. proportions of about fivev grams of solid cellulose acetate to 95 cc. of acetone gives a lacquer of the above type. The desired impenetrable surface coating is formed on the sides of the block III by dipping or immersing the block for fifteen seconds to a minute in the lacquer, then draining and wiping orshaking off excess lacquer. This fills the pores on the sides of the brush and solvent to a relatively low pressure I maythen be and 120 C.

the sides of the prevents exudation of the impregnant. Cellulose applied in thisv same manner also has given very good results. Other lacquers also block The chief requisite have proved successful when in relatively thin coatings. of the lacquer coating is that it must not react applied to the with the impregnant and must prevent exudation and scope ofrmy invention,

What I claim as new and .desireto secure by Letters Patent of the United States is:

I. An electrical contact; element including a porous block of finelydlvided electrically conductive material, at least a portion of said block being impregnated with a polyhydric' alcohol solulimited' to the particular ar-' trically conductive block by subjecting J sure, impregnating at claims to cover all m' iflcations wh'ich'do tact element including for the contact surface of said air drying lacquer coating on draining and by drying,

tion providing a lubricant for the contact surface of said element, and a coating on the sides of said block, said coating being impenetrable by said impregnant.

2. An electrical contact element including a porous block of finely divided material, at least a portion of said block being impregnated with an alcohol-ether solution providing a lubricant for the contact surface of said element, and a. thin coating on the sides of said block. said coating being impenetrable by said impregnant.

3. An electrical contact element including a porous block of finely div'ded electrically conductive material, at least a portion of said block being impregnated with a providing a lubricant for the contact surface of said element, and a lacquer coating on the sides of said block. 4. An electrical contact element including'a porous block of finely divided material at least a portion of said block being impregnated with a polyhydric alcohol solution providing a lubricant element, and an the sides of said block.

5. An electrical contact element including a porous block of finely divided material, at least a portion of said block being impregnated with a polyhydric alcohol solution providing a lubricant for the contact surface of said element, and a cellulose acetate lacquer coating on the sides of said block. g H 6. An electrical contact element including a porous block of finely divided material, at least a portion of said block being impregnated with a polyhydlic alcohol solution providinga lubricant for the contact surface of said element, and a cellulose nitrate lacquer coating on the sides of said block. v

7. The method of making an electrical contact element including forming a porous block, de- I gassing the porous block, impregnating .at least a part of the degassed porous block with of the impregnated block a relatively thin coating of material impenetrable by the impregnant.

8. The method of making an electrical contact element including forming a porous block or electrically conductive material, degassing the porous block by subjecting it to a relatively low pressure, impregnating at least a part of-the degassed porous block with nonaethylene glycol, removing, excess impregnant from the block, and applying to the sides of the block a relatively thin coating of material. impenetrable by the impresnant.

9. The method of making an electrical contact element including forming a porous block of elecmaterial, degassing the porous least a part of the degassed porou block with a p lyhrdric alcohol solution. removing excess impregnant from the block by and applying a relatively thin coating of lacquer block.

10. The method of making an electrical conforming a porous block of electrically conductive, material, degassing the porous block-by subjecting it to a relatively low pressure, impregnating at least a part of the degassed porous block with .a solution of non, aethylene glycol and polyoleiln glycol, removing excess impregnant from the block, app1ying a relpolyhydric alcohol solution a p lyhydric alcohol solution, and applying to the sides it to a relatively low pres-.

to the sides of the dried atively thin coating of sides of the dried block, and removing excess lacquer by wiping and by drying at a temperature of substantially between 75 and 120 C. for substantialiy an hour.

12; The method of making an electrical contact element including forming a porous block of electrically conductive material, degassing the porous block bysubjecting it to a relatively low pressure for from one to two hours,- impregnate .ing' at least a part of thet degassed porous block with a solution of nonaethylene glycol in benzene for from one to two hours, removing excess 'impregnant from the block by draining and by drying at a temperature between 70 and 120 CL, applying a relativelythin coating of lacquer to the sides of the dried block, and removing excess lacquer by wiping and by drying at a temperature 01' between 75 and 120 for-substantially an hour.

13. The method of making an electrical contact element including forming a porous block of electrically conductive material, degassing the pomaterial, degassing the pregnant from the block by draining and by drymg at a temperature [between 70 and 120 C.,

lacquer by wiping and by ture of between 75 an hour.

14. The method of making drying at a tempera.-

an electrical 'contact element including forming a porous block of 70 and 120 finely divided metallic and raphitic electrically j conductive material, degassing th porous block by immersing in a to solution of nonaethylene glycol in water and subjecting the block for one to two hours to a relatively low ressure such that the water of the with a 10% to 30% solution of nonaethylene glycol in water for fromone to two hours, re-

moving excess impregnant from the block by draining and by drying at a temperature between C., applying a relatively thin coating of lacquer to the sides of the dried block,

and removing excess lacquer by wiping and by l drying at a temperature 01f between and C. for substantially an hour. a 4

CHARLES G. VAN BRUNT.

and 120 C. for substantially 

